6,050 research outputs found
Contribution of Extragalactic Infrared Sources to CMB Foreground Anisotropy
We estimate the level of confusion to Cosmic Microwave Background anisotropy
measurements caused by extragalactic infrared sources. CMB anisotropy
observations at high resolution and high frequencies are especially sensitive
to this foreground. We use data from the COBE satellite to generate a Galactic
emission spectrum covering mm and sub-mm wavelengths. Using this spectrum as a
template, we predict the microwave emission of the 5319 brightest infrared
galaxies seen by IRAS. We simulate skymaps over the relevant range of
frequencies (30-900 GHz) and instrument resolutions (10'-10 degrees Full Width
Half Max). Analysis of the temperature anisotropy of these skymaps shows that a
reasonable observational window is available for CMB anisotropy measurements.Comment: 14 pages (LaTex source), 3 PostScript figures. Final version, to
appear in ApJLetters May 1. Expanded discussion of systematic error
Evaluation of aluminium-based coatings for cadmium replacement
Cadmium electroplating is widely used in the aerospace industry for the corrosion protection of aircraft components like fasteners manufactured from non corrosion resisting high strength steels. However, environmental and safety concerns over the high toxicity of cadmium and its compounds have led to the investigation of suitable replacements. Alternatives to cadmium should offer effective corrosion protection and have no detrimental effects on the steel substrate. Hydrogen is known to be absorbed during processes like electroplating, thus causing hydrogen embrittlement on high strength steel fasteners. Another source of hydrogen is the water reduction occuring in parallel with the corrosion of the coating, and thus causing reâembrittlement of the steel substrate. This study has investigated the effect of the application of two aluminiumâbased coatings, SermeTel CR984âLT and GalvanoâAluminium Alcotec, on the hydrogen reâembrittlement of high strength steels used for aerospace applications. Slow strain rate testing has been performed to study the effect of hydrogen on the reâembrittlement of the steel substrate as a result of the corrosion of the aluminiumâbased coatings in a variety of environments, such as NaCl solution, salt spray and marine atmosphere. Permeation measurements have been used to measure hydrogen uptake by unplated steel membranes potentiostatically charged at the potentials of the aluminiumâbased coatings, so as to simulate the amount of absorbed hydrogen due to their corrosion. Corrosion tests have been utilised to evaluate the performance of SermeTel CR984âLT and GalvanoâAluminium Alcotec.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
Undiagnosed dementia in primary care: A record linkage study
BackgroundThe number of people living with dementia is greater than the number with a diagnosis of dementia recorded in primary care. This suggests that a significant number are living with dementia that is undiagnosed. Little is known about this group and there is little quantitative evidence regarding the consequences of diagnosis for people with dementia.ObjectivesThe aims of this study were to (1) describe the population meeting the criteria for dementia but without diagnosis, (2) identify predictors of being diagnosed and (3) estimate the effect of diagnosis on mortality, move to residential care, social participation and well-being.DesignA record linkage study of a subsample of participants (nâ=â598) from the Cognitive Function and Ageing Study II (CFAS II) (nâ=â7796), an existing cohort study of the population of England aged â„â65 years, with standardised validated assessment of dementia and consent to access medical records.Data sourcesData on dementia diagnoses from each participantâs primary care record and covariate and outcome data from CFAS II.SettingA population-representative cohort of people aged â„â65 years from three regions of England between 2008 and 2011.ParticipantsA total of 598 CFAS II participants, which included all those with dementia who consented to medical record linkage (nâ=â449) and a stratified sample without dementia (nâ=â149).Main outcome measuresThe main outcome was presence of a diagnosis of dementia in each participantâs primary care record at the time of their CFAS II assessment(s). Other outcomes were date of death, cognitive performance scores, move to residential care, hospital stays and social participation.ResultsAmong people with dementia, the proportion with a diagnosis in primary care was 34% in 2008â11 and 44% in 2011â13. In both periods, a further 21% had a record of a concern or a referral but no diagnosis. The likelihood of having a recorded diagnosis increased with severity of impairment in memory and orientation, but not with other cognitive impairment. In multivariable analysis, those aged â„â90 years and those age
Dust Temperatures in the Infrared Space Observatory Atlas of Bright Spiral Galaxies
We examine far-infrared and submillimeter spectral energy distributions for
galaxies in the Infrared Space Observatory Atlas of Bright Spiral Galaxies. For
the 71 galaxies where we had complete 60-180 micron data, we fit blackbodies
with lambda^-1 emissivities and average temperatures of 31 K or lambda^-2
emissivities and average temperatures of 22 K. Except for high temperatures
determined in some early-type galaxies, the temperatures show no dependence on
any galaxy characteristic. For the 60-850 micron range in eight galaxies, we
fit blackbodies with lambda^-1, lambda-2, and lambda^-beta (with beta variable)
emissivities to the data. The best results were with the lambda^-beta
emissivities, where the temperatures were ~30 K and the emissivity coefficient
beta ranged from 0.9 to 1.9. These results produced gas to dust ratios that
ranged from 150 to 580, which were consistent with the ratio for the Milky Way
and which exhibited relatively little dispersion compared to fits with fixed
emissivities.Comment: AJ, 2003, in pres
Provenance of Eocene river sediments from the central northern Sierra Nevada and implications for paleotopography
Geochronology of fluvial deposits can be used to characterize provenance, the paleotopography of sediment source regions, and the development of regional drainage systems. We present U-Pb and (U-Th)/He ages of detrital zircon grains from Eocene gravels preserved in several paleoriver systems along the western flank of the central and northern Sierra Nevada. These ages allow us to trace the sourcing of detritus in paleorivers and to constrain the evolution of the Sierra Nevada range front. U-Pb zircon age distributions are bimodal, with a dominant peak between 110 and 95 Ma and smaller but significant peaks in the Middle to Late Jurassic, matching the predominant ages of the Sierra Nevada batholith. A small fraction (<6%) of grains has pre-Mesozoic ages, which consistently match ages from prebatholithic assemblages within the northern part of the range. (U-Th)/He ages of a subset of double-dated zircons cluster between 114 and 74 Ma and are consistent with batholithic (U-Th)/He cooling ages in the northern Sierra. Our results indicate that the Eocene river systems in the central northern Sierra Nevada likely had proximal headwaters and had relatively steep axial gradients, draining smaller areas than was commonly thought. This also suggests that the northern Sierra Nevada would have had an established drainage divide and would have acted as a major topographic barrier during the early to mid-Cenozoic. The data presented here support a model of the Eocene northern Sierra Nevada characterized by a western slope with a gradient broadly similar to that of today
A Comparison of Satellite-Derived Snow Maps with a Focus on Ephemeral Snow in North Carolina
In this paper, we focus on the attributes and limitations of four commonly-used daily snowcover products with respect to their ability to map ephemeral snow in central and eastern North Carolina. We show that the Moderate-Resolution Imaging Spectroradiometer (MODIS) fractional snow-cover maps can delineate the snow-covered area very well through the use of a fully-automated algorithm, but suffer from the limitation that cloud cover precludes mapping some ephemeral snow. The semi-automated Interactive Multi-sensor Snow and ice mapping system (IMS) and Rutgers Global Snow Lab (GSL) snow maps are often able to capture ephemeral snow cover because ground-station data are employed to develop the snow maps, The Rutgers GSL maps are based on the IMS maps. Finally, the Advanced Microwave Scanning Radiometer for EOS (AMSR-E) provides some good detail of snow-water equivalent especially in deeper snow, but may miss ephemeral snow cover because it is often very thin or wet; the AMSR-E maps also suffer from coarse spatial resolution. We conclude that the southeastern United States represents a good test region for validating the ability of satellite snow-cover maps to capture ephemeral snow cover
Is there Evidence for Flat Cores in the Halos of Dwarf Galaxies?: The Case of NGC 3109 and NGC 6822
Two well studied dwarf galaxies -- NGC 3109 and NGC 6822 -- present some of
the strongest observational support for a flat core at the center of galactic
dark matter (DM) halos. We use detailed cosmologically motivated numerical
models to investigate the systematics and the accuracy of recovering parameters
of the galaxies. Some of our models match the observed structure of the two
galaxies remarkably well. Our analysis shows that the rotation curves of these
two galaxies are instead quite compatible with their DM halos having steep
cuspy density profiles. The rotation curves in our models are measured using
standard observational techniques. The models reproduce the rotation curves of
both galaxies, the disk surface brightness profiles as well as the profile of
isophotal ellipticity and position angle. The models are centrally dominated by
baryons; however, the dark matter component is globally dominant. The simulated
disk mass is marginally consistent with a stellar mass-to-light ratio in
agreement with the observed colors. We show that non-circular motions combined
with gas pressure support and projection effects results in a large
underestimation of the circular velocity in the central kpc region,
creating the illusion of a constant density core. Although the systematic
effects mentioned above are stronger in barred systems, they are also present
in axisymetric disks. Our results strongly suggest that there is no
contradiction between the observed rotation curves in dwarf galaxies and the
cuspy central dark matter density profiles predicted by Cold Dark Matter
models.Comment: Accepted for publication in the ApJ. New discussion, figures and one
appendix. High resolution version
at:http://www.astro.washington.edu/octavio/N3109_paper.ps.g
Infrared Excess Sources: Compton Thick QSOs, low luminosity Seyferts or starbursts?
We explore the nature of Infrared Excess sources (IRX), which are proposed as
candidates for luminous L_X(2-10keV)>1e43erg/s Compton Thick (N_H>2e24cm^{-2}z\approx1z\approx2$ IRX population are not Compton
Thick QSOs but low luminosity [L_X(2-10keV)<1e43erg/s], possibly Compton Thin,
AGN or dusty starbursts. It is shown that the decomposition of the AGN and
starburst contribution to the mid-IR is essential for interpreting the nature
of this population, as star-formation may dominate this wavelength regime.Comment: Accepted by MNRA
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